Re: [GHC] #11508: QuickCheck application hangs with concurrent read/write of Chan

27 Mar 2016

      #11508: QuickCheck application hangs with concurrent read/write of Chan
-------------------------------------+-------------------------------------
        Reporter:  orion             |                Owner:
            Type:  bug               |               Status:  infoneeded
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:  x86_64
                                     |  (amd64)
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by erikd):

 If I change the program so that it no longer runs the tests via QuickCheck
 as follows:

 {{{
 {-# LANGUAGE OverloadedStrings, CPP #-}
 module Main where

 import Imports
 import Control.Concurrent
 import Control.Concurrent.Async
 import Data.ByteString

 instance Arbitrary ByteString where
   arbitrary = pack <$> arbitrary

 doFoo :: Bool
       -> Int
       -> ByteString
       -> (ByteString -> IO ())
       -> (IO ByteString)
       -> IO ByteString
 doFoo _ 0 g _ _ =
   return g

 doFoo b i g w r =
   if b then do
     w g
     doFoo False (i-1) g w r
   else do
     f <- r
     doFoo True (i-1) f w r

 prop :: ByteString  -> IO Bool
 prop x = do
   chan <- newChan
   let w s = writeChan chan s
       r   = readChan chan
   (y, z) <- concurrently (doFoo True 10 x w r) (doFoo False 10 x w r)
   return $ y == z

 main :: IO ()
 main = print =<< prop "Hello"
 }}}

 then when the program runs it terminates with:

 {{{
 properties: thread blocked indefinitely in an MVar operation
 }}}

 Interestingly, it does that regardless of whether the program is compiled
 with `-threaded` or not.

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11508#comment:13
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler